In lenticular type three-dimensional (3-D) photography, a plurality of two-dimensional (2-D) views of the same scene are taken from a number of horizontally spaced vantage points, and a series of 2-D images is then compressed and printed at the focal plane on the emulsion of each of the lenticules of the lenticular print film to form a 3-D composite image of the scene.
When a person is viewing a 3-D photograph, the right and left eyes see two image bands which form a stereo pair. The spatial parallax between the images of the stereo pair reconstructs the spatial effect and the sensation of depth to the photographed scene.
The method of taking and composing lenticular type 3-D photographs is explained in some of the following publications.
N. A. Valyus in Stereoscopy (The Focal Press 1962) at pages 195-205 discloses the basic method of taking and printing 3-D photographs on lenticular print material.
Rudolf Kingslake in Applied Optics and and Optical Engineering (Academic Press 1965) at pages 108-116 also discusses some of the basic principles involved in lenticular three-dimensional photography.
Takanori Okoshi in Three-Dimensional Imaging Technique (Academic Press 1972) at pages 61-95 discusses a number of techniques for taking three-dimensional photographs.
The following U.S. patents are of interest in connection with three-dimensional photographic techniques.
U.S. Pat. No. 3,895,867 (Lo etal) PA0 U.S. Pat. No. 3,953,869 (Lo etal) PA0 U.S. Pat. No. 3,960,563 (Lo etal) PA0 U.S. Pat. No. 4,037,950 (Lo etal) PA0 U.S. Pat. No. 4,063,265 (Lo etal) PA0 U.S. Pat. No. 4,120,562 (Lo etal) PA0 U.S. Pat. No. 3,482,913 (Glenn) PA0 U.S. Pat. No. 3,518,920 (Glenn)
A major difficulty in lenticular type 3-D photographs is that the 3-D photograph frequently has either too little three dimensional effect or the image is out of focus because of too little or excessive spatial parallax between the stereo pairs. Parallax is the apparent shift in position of an element of an object field due to the relative change in position of the element and place from which the element is viewed. The spatial parallex on a lenticular 3-D photograph is simply the distance on the photograph between the images of the same object of a stereo pair.
U.S. Pat. No. 3,960,563 (column 12, line 47 through column 13, line 43) suggests that the maximum spatial parallax between two adjacent images should be controlled not to exceed five lenticules width if the width of the lenticule in the picture is greater than 5 mils, or not to exceed ten lenticules width if the width of the lenticule is smaller than 5 mils. U.S. Pat. No. 4,037,950--Lo etal (column 12, lines 28-61) also takes this same position as does U.S. Pat. No. 4,063,265--Lo etal (column 12, lines 31-64).
This technique of trying to control the spatial parallax between an image pair by setting the number of lenticules between an image pair of the same object is not effective under the following circumstances:
1. When using print materials of different lenticule width.
For example, when taking a 3-D photograph, if the lenticule wtdth of 1 mm is used, the resulting maximum permissible spatial parallax is 5 lenticule units in accordance with the above technique. However, if this same photograph is printed with the same degree of magnification on print material having a lenticule width of 0.125 mm, the resulting parallax will become 40 lenticule units which is four times the maximum permissible spatial parallax, and the 3-D photograph is totally out of focus.
2. Changing the magaification when printing a 3-D photograph.
For example, if the lenticule width is 0.15 mm (greater than 5 mils) and the photograph is magnified three times, the maximum permissible spatial parallax is five lenticule units. However, if this same photograph is printed with a magnification of fifteen times, then the parallax will become 25 lenticule units which is five times the maximum permissible spatial parallax with the photograph being out of focus.
3. When printing photographs of different size.
If 3-D photographs of different sizes are made on the same type of print material with the same lenticule width and having the same maximum parallax according to the above limitation, the 3-D effect on the photographs of different size will not be consistent as larger 3-D photographs must be viewed from a greater distance. The larger photographs require more spatial parallax in order to obtain the same 3-D effect. 3-D photographs of smaller size are viewed at a closer distance and require less spatial parallax in order for the eyes to fuse the two images together.